= Rain gauge
A <rain gauge> measures precipitation collected over a known horizontal area. The reported rainfall depth is collected liquid volume divided by collector area: $h=V/A$. A tipping-bucket gauge converts repeated fixed-volume tips into accumulated depth; a weighing gauge measures collected <mass>.
Wind can deflect drops around the opening, and evaporation, splashing or freezing can bias the result. A gauge samples one location, so its reading need not represent a whole catchment during spatially uneven rain. The instrument <geometry> and exposure are therefore part of interpreting the <observation>.
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